Electrohydraulic sterilizing apparatus



Original Filed Feb /n venfor Mar/0n Allen His Afro/nay.

United States Patent 3,522,167 ELECTROHYDRAULIC STERILIZING APPARATUS Merton Allen, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Original application Feb. 2, 1965, Ser. No. 429,817. Divided and this application Oct. 2, 1967, Ser. No. 672,127

Int. Cl. Hc 1/00; A611 3/00; H01t 13/20 US. Cl. 204-323 4 Claims ABSTRACT OF THE DISCLOSURE An apparatus is disclosed comprising a chamber adapted to contain a substantially non-compressible dielectric liquid suspension of microorganisms and an electrode structure comprising a central rod-like conductive body surrounded by a tubular dielectric insulator which is encased within a tubular conductive body providing a working tip portion in the interior of said chamber. The dielectric insulator is made from glass fiber-reinforced polymeric material. When the chamber is filled with the liquid, and a spark discharge is generated between the electrode portions of the working tip, steep pressure or shock waves and chemically reactive species are generated which are effective to kill the microorganisms without destroying their antigenicity, enabling them to be used in the production of vaccines or bacterins.

This application is a divisional of copending application Ser. No. 429,817, filed Feb. 2', 1965 in the name of the present inventor, assigned to the same assignee, from which this application has been divided. The disclosure of said application is incorporated herein by reference.

This invention relates to the production of antigens in the manufacture of vaccines, and in particular, to an electrohydraulic sterilization apparatus for causing destruction of the viability of microorganisms without destroying the antigenicity thereof.

The antibody-producing mechanism in animals and humans is capable of producing immunization against certain diseases and infections such as diphtheria, smallpox, tetanus, measles and poliomyelitis. The antibody-producing mechanism is stimulated by the injection or introduction into the body of suspensions of living or killed microorganisms which cause the particular disease or infection. These suspensions of microorganisms, used for immunization purposes, are called vaccines. Injection of killed microorganisms is the preferred manner to stimulate immunity since the use of vaccines containing weakened but live microorganisms is not always sufliciently safe for human immunization.

The sterilization or killing of the particular microorganism to be employed in the vaccine is conveniently accomplished by one of two methods. In the first method, a suspension of a selected microorganism is heated at a temperature high enough to kill but not sufficiently high as to cause drastic changes in the antigens which are 'the operative substances in the vaccine. The antigens stimulate the formation of antibodies within the animal or human such that the antibodies can then react with that particular antigen upon subsequent exposure to such disease or infection. Heating at 60 C. for one hour is usually employed for non-sporulating organisms. In the second and sometimes preferable method, a chemical such as 1.0% Formalin is added to the microorganism suspension and thence allowed to stand at 37 C. for 12 hours. After the microorganisms have been killed, the chemical-microorganism suspension is chemically purified by being centrifuged and washed several times with an 0.9% .sodium chloride solution. For both of the conventional methods 3,522,167 Patented July 28, 1970 the vaccine is thence suspended in saline and diluted (standardized) so that the dose to be used to combat the disease or infection will be contained in 1 or 2 milliliters of liquid. After standardization, it is checked for sterility and a preservative such as 0.5% (final concentration) phenol or 0.01% (final concentration) merthiolate is added. In the case of soluble vaccines such as toxins, toxoids or various protein solutions, they are conventionally sterilized by filtration through a Seitz or Berkefeld filter. Ethylene oxide is sometimes also used for sterilization of some soluble vaccines.

The heating method employed for killing the microorganism is a very sensitive method and many microorganisms, particularly spore formers, cannot be treated this way. Further, the heat is likely to diminish the immunizing power of the antigens so produced. The second or chemical method for killing the microorganisms must be carefully chosen since some of the chemical disinfectants employed combine with the bacteria protein to form complexes. Further, the addition of Formalin does not work satisfactorily for certain microorganisms and is a time consuming process as well as requiring subsequent washings to chemically purify the formed vaccine to make it safe for injection. Thus, in view of the limitations of the conventional methods for killing microorganisms employed in vaccines, there is a need for providing a new process to accomplish this result.

A recently developed concept, conveniently named electrohydraulics is known to have the ability of killing many strains of microorganisms. The electrohydraulic concept comprises a controlled release of stored electric energy into a relatively noncompressible and dielectric fluid medium which comprises the material to be acted upon. The controlled release of this stored energy in the fluid medium generates a controlled steep pressure or shock wave therein of sufficient intensity and a multitude of chemically active species to cause destruction (kill) of the microorganisms and thereby accomplish a sterilization process. The intensity and steepness of the pressure or shock wave which accomplishes much of the useful work in the fluid medium may be controlled by controlling the magnitude and other parameters of the stored electric energy or its manner of transmission into the fluid medium.

Therefore, one of the principal objects of my invention is to provide a new sterilization apparatus for killing microorganisms in the preparation of vaccines.

Another object of my invention is to provide such apparatus utilizing the electrohydraulic concept for the killing action.

A still further object of my invention is to provide an improved electrode structure forming the spark gap in the electrohydraulic equipment employed to obtain the microorganism kill.

Another object of my invention is to provide an improved electrohydraulic chamber-electrode structure in the electrohydraulic equipment.

Briefly stated, and in accordance with my invention, my process for producing antigens in the preparation of vaccines employs the electrohydraulic concept for killing (sterilizing) particular microorganisms in a fluid medium. A predetermined amount of a selected living microorganism is added to a predetermined amount of a selected sterile liquid to obtain a desired concentration of living microorganism suspension, generally in the range of 10 microorganisms per milliliter. The living microorganism suspension is thence passed into a sterilized electrohydraulic chamber in which the suspension is confined for the duration of the sterilization process. One, or a predetermined plurality of electrohydraulic shocks (discharges) are thence initiated within the microorganism suspension contained in the chamber by discharging a desired level of stored electric energy (one discharge per shock) into a spark gap immersed therein. The electrohydraulic action causes destruction of the viability of the microorganisms without destroying the antigenicity thereof to thereby sterilize the microorganism suspension and form an antigen suspension therefrom. The antigen suspension is thence passed from the electrohydraulic chamber and processed in a conventional manner (checked for sterility and a preservative added) to be suitable for the end use thereof as a vaccine in the injection of animals or humans for providing immunization against a selected disease or infection.

The spark discharge electrode employed to form the spark gap in the electrohydraulic equipment includes a prefabricated tube constructed from a laminate of spirally wound porous sheet material impregnated with a suitable polymer to obtain a tubing having high strength, high electric-insulating properties and low moisture absorption. The prefabricated tube is employed in a coaxial electrode structure wherein such tube is the insulator separating a high voltage center electrode from a hollow coaxial outer ground electrode of my electrode structure.

The features of my invention which I desire to protect herein are pointed with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, and wherein:

A side view, in section, of a spark discharge electrode constructed in accordance with my invention and sealed in place within an electrohydraulic chamber is shown.

The electrohydraulic concept is derived from the sudden release of a relatively large magnitude of electric energy within a relatively noncompressible fluid dielectric (but not absolutely nonconductive) medium. The electric energy is, in general, obtained from a conventional electrical power supply adapted to supply direct current power at a voltage in the kilovolt range. The electric energy is initially stored in a capacitor which is charged from the power supply. The electric energy stored in the capacitor is subsequently discharged into a spark gap formed by at least one electrode immersed in the fluid which is confined in a container described as an electrohydraulic chamber. The discharge is produced in a series electrical circuit which includes the capacitor, a switching means for completing the circuit, the spark gap and suitable electrical conductors for transmitting the discharged energy to obtain desired characteristics of the steep pressure or shock wave generated in the fluid upon release of electric energy across the spark gap. The shock wave may be of suflicient intensity, and a multitude of chemically active species are also formed, to cause destruction (kill) and sterilization of many strains of microorganisms in the fluid. Microorganisms as described herein are of the type such as bacteria, virus, rickettsiae, fungi and protozoa. Since virus is a nonliving microorganism, it should be understood that the expression destruction or kill as applied to the broad class of microorganisms implies inactivation of the virus.

While the exact mechanism of electrohydraulic energy conversion and microorganism destruction is a complex phenomenon not fully understood at the present, the following explanation of the operative principles is offered to explain such phenomenon. Delivery of the high voltage electric energy to the spark gap is at a faster rate than the fluid mediums ability to absorb the heat generated thereby. Consequently, the fluid medium is vaporized in the gap vicinity undergoing at least partial ionization. Subsequent expansion of the plasma bubble during the short time interval of energy release produces a shock wave in the remaining noncompressible fluid environment.

-In the particular case wherein water is the fluid medium, the destruction (sterilization) of the microorganisms therein is attributed primarily to the chemically active species formed, the ultraviolet energy release, the high localized temperature, the intense pressure or shock wave generated within the water and the extreme turbulence created thereby, and phase changes caused by this intense pressure or shock wave. The chemically active species formed by the spark discharge appear to play a significant role in destroying the microorganisms as does the shock wave. The active species formed may be described as the decomposition products of the liquid media, for instance in water, hydrogen and the hydroxyl radicals and also nascent hydrogen and oxygen, hydrogen peroxide and ozone. The phase changes occurring due to the shock wave are the change from the water liquid to a gas or vapor phase or even to a solid ice phase at such high pressures for an instant of time. The values of the energy controlling parameters such as voltage, capacitance, resistance and inductance, and certain design parameters such as electrode gap, liquid volume, and liquid physical and chemical properties can be varied according to the particular microorganisms to be treated. Although the interrelation between parameters is complex, and at present not fully understood, there are apparent optimum conditions for each particular microorganism and liquid media which result in efliective microorganism kill (sterilization). The energy for producing such sterilization can range as low as a fraction of a watthour to as high as several hundred watthours per gallon of microorganism suspension to be treated.

In accordance with my invention, I produce the particular antigens which are used in the vaccine to be subsequently available for injection into an animal or human, by employing the electrohydraulic concept to kill selected antigen-producing microorganisms. The selected microorganism employed may be grown by any of the known techniques and if grown upon a solid surface the resultant culture is washed from the surface upon which the growth evolved to obtain a living microorganism suspension. In many vaccine preparations, the liquid employed to wash the culture from the surface is a suitable buffer employed as the carrier for the microorganism suspended therein and as a means for stabilizing the pH of the suspension. The process for producing the antigens is accomplished in the following manner. A predetermined amount of a selected living microorganism suspension is added to a predetermined amount of a selected sterile fluid to obtain a desired concentration of living microorganism suspension, generally in the range of 10 microorganisms per milliliter. The fluid is not heated and may comprise any suitable fluid used in vaccines such as saline, serum, distilled sterile water or other serological liquids. In the case of distilled sterile water or other dielectric fluids, a predetermined amount of a suitable buffer is also added thereto to cause the dielectric fluid to have suflicient electrical conductivity for obtaining eflicient generation of the electrohydraulic shocks within the fluid. The desired concentration of living microorganism suspension is thence passed into a sterilized electrohydraulic chamber in which the suspension is confined for the duration of the microorganism sterilization process. The capacitor (or capacitor bank) of the electrohydraulic equipment is thence charged to a desired level of electric energy from a direct current electrical power supply operable in the kilovolt range and which may be of conventional design. A single or predetermined plurality of electrohydraulic shocks, one shock for each charging and discharge of the capacitor, is thence initiated within the microorganism suspension contained in the electrohydraulic chamber by discharging the electric energy stored in the capacitor into a spark gap immersed within the microorganism suspension. The electrohydraulic shocks and attendant chemically active species effectively kill or sterilize all of the microorganisms within this suspension in the manner hereinabove described to cause destruction of the viability of the microorganisms without destroying the antigenicity thereof. The parameters necessary for total kill of the microorganisms present is obtained by prior tests of electrohydraulic destruction of the various microorganisms employed in the vaccines to be produced. Thus, an optimum combination of power supply voltage, level of electric energy per electrohydraulic shock, number of electrohydraulic shocks, spark gap and capacitor size may be determined by prior tests to obtain complete kill for predetermined volumes and concentrations of each particular type of microorganism suspension of interest. At the termination of the electrohydraulic shocks, the sterilized microorganism suspension (the antigen suspension) is passed from the electrohydraulic chamber to a suitable sterilized container for storage of the vaccine. The vaccine is thence checked for sterility and may subsequently be processed in a conventional manner, such as by the addition of a suitable preservative or the provision of a suitable temperature environment, and stored until such time that it is to be used as a vaccine in the injection of animals or humans for providing immunization against a selected disease or infection.

A description of the process for preparing E. coli vaccine in accordance with the electrohydraulic process of my invention is more fully described in the copending application, previously identified.

In the drawing there is shown an electrohydraulic chamber and a spark discharge electrode suitable for the generation of the electrohydraulic shocks employed in my sterilization process. The electrohydraulic chamber comprises top and bottom cover members 1 and 2, respectively, the cover members enclosing a hollow cylindrical side member 3 on opposite ends thereof to provide the sealed electrohydraulic chamber therein. Members 1, 2 and 3 are made of stainless steel, brass or other suitable strong material that is electrically conductive and nonreactive with the vaccines to be produced within the chamber. Suitable nuts and bolts 4 may be employed to retain the cover members in good contact with cylindrical member 3 and an O-ring type gasket 5 and 6 may be employed to insure a proper seal of top cover member 1 and bottom cover member 2, respectively, with cylindrical member 3. A first threaded plug 7 located Within top cover 1 is employed as a fluid inlet for passing the living microorganism suspension into the electrohydraulic chamber. A second threaded plug 8 located within bottom cover 2 is employed as a fluid outlet for passing the antigen suspension from the electrohydraulic chamber. The spark discharge electrode, illustrated as a whole by numeral 9, is characterized by being threaded on its outer cylindrical surface. Electrode 9 is supported within top cover member 1 and sealed thereby by means of nut 10, locking nut 11 and O-ring12. The O-ring 12 seals the threads of electrode 9 to the threads of nut to prevent escape of any fluid from the electrohydraulic chamber.

The structure of spark discharge electrode 9 as illustrated in the drawing forms a part of my invention and will now be described in detail. Electrode 9 is of cylindrical coaxial structure and has utility in electrohydraulic applications such as my antigen-producing process wherein the discharged electric energy is from about 50 to less than 5,000 joules per discharge. This particular electrode has been used at discharge repetition rates as high as 30 discharges per second, although this is not to be construed as the upper limit of operation. Unlike other spark discharge electrodes employed in electrohydraulic apparatus, the structure of electrode 9 does not rely on a cast and bonded ceramic (particulate mixed with liquid and cast in place) for the coaxial and annular dielectric insulator separating a longitudinally extending solid rod high voltage center electrode 13 from a hollow coaxial outer ground electrode 14. In the embodiment of FIG. 1, the insulator 15 comprises a prefabricated tube made of bonded multi-layer spirally Wound porous sheet material, impregnated with a suitable polymer resulting in a tubing having high strength, high electric insulating properties and low moisture absorption. In a preferred embodiment of insulator tube 15, I employ a prefabricated multilayer (laminate) spirally wound fiber glass cloth bonded with an epoxy resin (glass-epoxy NEMA Grade G-10). Other glass cloth, fiber, paper, or polymer cloth bonded with polymer and other resin systems such as phenolics may also be employed. The prefabricated insulator tube 15 has an inner diameter which is approximately 4 to 10 mils larger than the diameter of high voltage center electrode 13 and an outer diameter approximately 4 to 10 mils smaller than the inner diameter of hollow coaxial ground electrode 14. The thickness of the wall of prefabricated insulator tube 15 thus approximates the gap across which a spark is ignited upon the discharge of electric energy previously stored in the capacitor (not shown) of the electrohydraulic apparatus.

High voltage center electrode 13 is constructed of a suitable good electrically conductive metal, is cylindrical in shape and smooth surfaced. For the sterilization ap plication, solid rod electrode 13 may conveniently be manufactured from a copper-silicon alloy designated Everdur 1010 which exhibits high tensile strength and good arc-resistance, thereby resulting in minimum tip erosion. The outer hollow ground electrode 14 is also made of a good conductive metal, is cylindrically shaped and can be threaded for part or all of its outer surface as illustrated in FIG. 1. For the sterilization application it has been found convenient to manufacture the ground electrode of 606 1-T6 aluminum alloy. Obviously, the outer surface of tubular ground electrode 14 may be smooth and not threaded and appropriately sealed to the top cover member, if desired. The 4 to 10 mil spacing between each of the adjacent members 13, 15 and 14 is for holding a cement which rigidly bonds the three coaxial parts together to form a unitary solid construction. The cement 16, 17 can be of any commercial material suitable for bonding the insulator tube 15 to the high voltage rod electrode 13 and tubular ground electrode 14, and being low in water absorption. A particular cement that was found to be satisfactory is a commercial two part epoxy cement Barco-bond MB10OX.

For proper manufacture of spark discharge electrode 9, all of the mating parts 13, 14 and 15 are cleaned and degreased by attrition and solvent washing and are air dried. The outer surface of the dielectric insulator tube 15 is coated with the cement and carefully inserted into the tubular ground electrode 14. When the tubular body 14, 15 is reasonably dry, the center high voltage rod electrode 13 is coated with cement and inserted into the center hole of the insulator tube 15. The center high voltage rod electrode 13 should extend above the top end of insulator tube 15 a suflicient distance to allow a high voltage electrical connection to be made thereto. Insulator tube 15 should extend above the top end of outer ground electrode 14 a sufiicient distance to prevent flash-over and surfacetracking from taking place. The electrical connection 18 and an electrical connection 19 to ground electrode 14 can be made by any known method for the connection of a high voltage discharge circuit (not shown) to spark discharge electrode 9. After assembly and curing or drying of the cement, the bottom end of electrode 9 is dressed down such that the working tip of high voltage electrode 13 extends out from A to 4 inch and the insulator tube 15outer ground electrode 14 form a flat surface perpendicular to the electrode axis. Arc discharge occurs between the extended inner high voltage electrode 13 and outer ground electrode 14 over the bottom surface of insulating tube 15. Spark discharge electrode 9 can be made in any desired length and the electrode gap distance (space occupied by insulator tube 15 and the two cement layers 16, 17) can be dimensioned as required comensurate with the dielectric properties of the insulating material of insulator 15 and the voltage and fluid medium to be used. Gaps of from to inch have been fabricated and used but these dimensions do not constitute an upper or lower limit of the gaps which may be employed. The

wall thickness of outer ground electrode 14 may be of any desired dimension provided it is sufficiently strong to resist rupture by electrohydraulic shock wave action. The shape of the electrohydraulic working tip is maintained by periodic reworking to the shape hereinabove described. Many such reshaping processes can be performed and the depth of insert of electrode 9 advanced through top cover member 1 in order to keep the tip (bottom end of high voltage electrode 13) positioned a desired distance within the chamber.

From the foregoing description, it can be appreciated that the invention makes available an electrohydraulic apparatus for producing antigens in the preparation of vaccines by means of electrohydraulically treating a desired concentration of selected living microorganisms suspension to cause destruction of the viability of the microorganisms without destroying the antigenicity thereof. The invention also makes available an improved electrohydraulic chamber and electrode structure which forms the spark gap of the electrohydraulic apparatus. The advantages of the electrohydraulic process for producing antigens are numerous and have been described hereinabove and in the previously referenced application but it bears repeating that the subsequent chemical purification employed in conventional chemical methods for killing the microorganisms is not required with the process, the use of external heat required in another conventional process is also not required with the process, and the process obtains the microorganism kill in a much shorter time interval (in the range of a few seconds to a few minutes, depending on repetition rate of electrohydraulic discharge) than either of the two conventional processes. The process permits complete sterilization of the microorganism suspension within seconds as opposed to one or more hours required by conventional processes.

Having described the electrohydraulic process for producing antigens, the improved electrohydraulic chamber and the improved electrode structure employed in the electrohydraulic equipment for producing such antigens, it is believed obvious that modification and variation of the invention is possible in the light of the above teachings. Thus, the process and apparatus is not limited to the E. coli vaccine disclosed but is applicable to all known vaccines made from microorganisms described as bacteria, virus, rickettsiae, fungi and protozoa. It is, therefore, to be understood that changes may be made in the particular electrode and chamber structure as described which are within the full intended scope of the invention as defined by the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A spark discharge electrode for use in an electrohydraulic chamber comprising a longitudinally extending solid rod of electrically conductive material,

a hollow member of electrically conductive material 8 coaxial with said solid rod, said hollow coaxial member having an internal opening larger than the trans verse dimension of said solid rod thereby defining a continuous annular space between said hollow member and solid rod, and

a prefabricated tube of electrically nonconductive material occupying the annular space and bonding said solid rod to said hollow member to form a unitary solid construction, said prefabricated tube being made of a bonded multi-layer spirally wound porous sheet material made from glass fibers and impregnated with polymer resulting in a tubing having high strength, high electric insulating properties and low moisture absorption.

2. A spark discharge electrode assembly having a working tip portion immersed in a substantially non-compressible working fluid and a terminal portion, which comprises a longitudinally extending metal rod, a hollow coaxial metal sheath concentrically positioned with respect to and substantially coextensive with said rod to define a continuous annular space, a tubular member composed of a glass fiber reinforced organic polymeric resin dielectric material occupying said annular space and bonded to said sheath and said rod to form a unitary solid construction for substantially the entire length of the electrode assembly, said tubular member being a laminated structure comprising a plurality of substantially identical layers, each layer being impregnated with said resin and adjoining layers being bonded together thereby support means providing an aperture through which said electrode assembly extends, and means for adjustably securing said electrode assembly at a point between said working tip and said terminal portion to said support means.

3. The electrode assembly recited in claim 1 wherein said tubular member is composed of a prefabricated tube.

4. The electrode assembly recited in claim 3 wherein said prefabricated tube comprises a bonded multilayer spirally wound porous sheet material impregnated with said organic polymeric resin dielectric material.

References Cited UNITED sTATEs PATENTS 1,119,674 12/1914 Besson 313-131 2,741,716 4/1956 Arthur et al. 3l3-l20 2,803,771 8/1957 Moore 313- 2,920,223 1/1960 Peras 313-131 2,931,947 4/1960 Fruengel 315-241 3,174,025 3/1965 Johnson 313-2315 3,354,344 11/1967 Schrom 313-130 ROBERT K. MIHALEK, Primary Examiner US. Cl. X.R. 

